Recent legislation aimed at improving aircraft security, particularly to reduce the threat posed by hi-jacking, requires the cockpit door to be closed and locked during a flight to prevent unauthorised access to the cockpit. During a flight, communications between the flight crew and the cabin crew are normally via an onboard interphone or intercom system by means of which information can be passed to and from the cockpit without requiring access to the cockpit. While this form of communication is satisfactory under normal flight conditions, it may not be possible for the cabin crew to use the interphone or intercom system to alert the cabin crew to a potentially dangerous situation in the passenger cabin, for example the cabin crew may be overpowered and prevented from accessing the interphone or intercom system in a hi-jack situation.
Accordingly, there is a need for a system that allows the cabin crew to be able to alert the flight crew to a potentially dangerous situation in the cabin without the passengers being aware that the flight crew have been alerted.
It has already been proposed, for example in U.S. Pat. Nos. 6,980,104 and 6,819,624 to employ systems in which the cabin crew are provided with portable transmitter units that can be worn or carried in a concealed location, for example in a pocket, and can be actuated in an emergency to transmit a signal to a receiver unit to produce a visual and/or audible warning in the cockpit of the existence of a potentially dangerous situation in the cabin.
With these portable transmitter units, the cabin crew can provide a discrete warning to the flight crew that there is a problem in the cabin. However, the information available to the flight crew from such visual and/or audible warning is limited. In particular, the signals transmitted from the portable units in these systems do not enable the flight crew to determine the position of the problem in the cabin.
Accordingly, there is a need for a system that not only allows the cabin crew to alert the flight crew when a problem arises but also identifies the actual position of the problem in the aircraft. This is particularly desirable in larger aircraft, especially multi-deck aircraft where it may be possible for the flight crew to remotely isolate an area of the cabin in which there is a problem from the rest of the cabin and reduce the threat or risk to the safety of the aircraft.
It has already been proposed in U.S. Pat. No. 6,819,264 to provide the portable transmitters with unique identification codes that enable the flight crew to know the transmitter from which the warning signal has come. However, this does not provide an indication of the position of the problem as the flight crew member carrying the transmitter can move around the aircraft and may be at any position within the cabin when the alert signal is generated.
It has also been proposed in U.S. Pat. No. 6,819,264 to mount additional buttons at concealed locations within the cabin that can be actuated by the cabin crew to alert the flight crew to a problem and are provided with unique identification codes that enable the flight crew to know the position of the button that has been actuated. However, there may be circumstances in which the cabin crew are prevented from accessing and actuating such hidden buttons to warn the flight crew. Also movement of the cabin crew to the positions where the buttons are hidden may alert the people causing the disturbance that an alert has been sent to the flight crew.